Resilient bushing



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ATTORNEYS Patented 'Api'. 26, 1938 PATENT o1=1=1cE RESILIENT RUSHING Oscar B. Welker, Middletown, Conn., assignor to Albert R. Teare, Cleveland, Ohio, Trustee Application December 15, 1936, Serial No. 115,941

2 Claim's.

This invention relates to improvements in resilient connections which embody inner and outer rigid members and an intermediate layer of rubber or other elastic material and pertains 5 particularly vto resilient stock which is used for making the finished article. The present application is a continuation in part of my copending application, Serial No. '76,392 filed April 25, 1936.

Many forms of elastic connections, or bushings of the type referred to have been placed upon the market, but experience has shown that there are certain objections inherent in them. For example, in one form, the hollow rubber tube or sleeve has been assembled by first compressing it by inserting it into the outer tube and then further compressing it by the use of an expanded mandrel before the inner tube is inserted into place. The resulting connection is thereby limited in length and the stresses are distributed unequally from one end to the other.

Another form of bearing has been made by curing the rubber between concentric tubes. The shrinkage of the rubber during the cooling operation is then depended upon to place it under tension. As a result, the rubber is unable to withstand very much repeated torsional movement under load. Moreover, the rubber, being under tension, deflects more than under compression, thereby allowing the inner tube to move more readily out of center under dead load.

In making a connection of this type, it is important that the rubber be placed under a fairly high degree of stress and that the stresses be distributed uniformly throughout the rubber, for this uniform distribution results in greater frictional engagement with the inner and outer members and a longer life of the rubber. An effort to accomplish this result has included a method of manufacture in which the rubber sleeve has been slipped onto an inner tube for a portion of its length and then compressed by reducing the diameter of the outer tube. This method, however, di'd not permit a connection to be made in unlimited lengths. Moreover, it did -not distribute the stresses uniformly throughout the length of the connection.

Still another effort to obtain the desired degree of compression has been to mount the rubber sleeves in tandem between the inner and outer tubes, and then to draw them together axially by the use of bolts. of manufacture, the rubber is not uniformly compressed for the greateststress is at the ends where the compressive force is applied.

A further effort to overcome the difliculties Under this method (Cl. .Z9-88.2)

enumerated has included the curing of a mass of rubber to the inner member and then forcing the assembly endwise into an outer member. Under such practice, however, the rubber cannot flow on the bonded area and hence most of the flow takes place on the unbonded area, and hence throughout the length the stresses are unequally distributed. A further objection to the curing operation is the fact that it is too expensive to be practical and that the length of bushing pro lduced is limited to very small sizes.

An object of my invention is to make a resilient stock that may be vused in a satisfactory manner for distributing resilient connections, wherein an intermediate layer of elastic material is so stretched at the time of its assembly between the inner and outer tubes, that the stresses are uniformly distributed throughout the length of the material.

Referring now to the drawings, Fig. l is a top plan view of a machine for making the resilient connections in accordance with my invention; Fig. 2 is a vertical section taken on the line 2 2 in Fig. 1 and shown on a scale larger than that of Fig. 1; Fig. 3 is an end view of the torsional bushing; Fig. 4 is a section taken on the line 4-4 in Fig. 3; Fig. 5 is a section showing a modified form of construction of the Stock from which the elastic sleeves are made; Fig. 6 is a side elevation partly in section of the rub-v ber stock; Fig. 7 is a side elevation of the machine; Figs. 8, 9 and 10 are sections taken on the correspondingly numbered lines in Fig. 1; Fig. 11 is a side elevation of an assembled unit before the sections have been cut therefrom; Fig. 12 is a section taken through an article embodying a modified form of the invention; Fig. 13

is a diagram showing a stress-stretch curve of rubber that is usually used in making torsional connections, and Figs. 14 to 20 inclusive; illustrate a modified form of the stock from which the elastic sleeves are made.

In Figs. 3 and 4, the resilient connections' which are made in accordance with my invention comprise an inner member lll, an outex` member ll andan intermediate member l2, all of which are shown as being cylindrical in shape and as having a common axis. The inner and outer members are preferably made of metal, while` the intermediate member is made of elastic material, such as rubber. It is understood that the inner member may be either tubular or a solid shaft of cylindrical shape or even that of a polygon, and that the outer member may be any vobject which has an inside cavity of a cylindrical shape, or even that of a polygon. The present application is concerned with rubber stock that is used for making the elastic sleeve.

The preferred mannerl of carrying out my 5 invention comprises the formation ofrubber stock into a long tube, the body of which is indicated at I5. One end of the tube is closed and the .opposite end is open.` The closed `end in one form of the invention may be formed by a plug i6, the outer end of which is reduced and is closely embraced by the stock. A ring I'I embracesthe stock at the reduced neck and cooperates with-the plug to impart strength to the stock at the closed end, so as to 'enable it to withstand the stresses that are incident to the stretching operation. The inner diameter of the stock is substantially equal to the outer diameter of the inner member l0, while the outer'diameter' of the stock is largerthan -the inner diameter of the member Il. Consequently it is necessary to reduce'the wall thickness of the stock, and

this I accomplish by stretching it duringthe assembly operation.

'I'he method by which I insert the elastic sleeve v between the inner and outer members comprises the insertion `of a long continuous tube lla into the stock until the forward end ofitengages an annular' shoulder 2l at the inner end of the plug I 8. 'I'he assembled unit is then placed in a machine and moved in an axial direction through a forming die 25,) which partially reduces the diameter of the rubber-sleeve from which it is passed into the tube Ila, which fur- -ther reduces it to the iinishedsize. The tube outer member Ii of the finished bushing.

'I'he machine which I have shown for 'st ingthe rubber during the inserting operation. may comprise an open frame which has sides Il and ends-Ii and Il respectively. Between the ends there is a 'cross-member Il, which supportsthe die 2l and there are other cross members y22, and 2l, each of which supports one end of a tube Ila. In the illustration shown, the end member functionslikewiseasasuppo for one of the tubes Ila. While'I have ill ted the machineas supporting tubes Ila in tandem relationship, it is to be understood that ,besplinedtoake'ylinoneofthebearingcaps' 1l. The spindle may Vhave one end thereof connected to a carriage Il that is mounted for movement along the members el.A The connection is illustrated in detail in Fig. 10 wherein theendofthespindlehasaflangellthatfitsloosely-into an opening Il in a plate 21 that is fastened totlie carriage. The carriage isl pro- 'vided with a saddle 42 in which 'the rearward end of the tube Ila is adapted. to be supported.

U-shaped so that e tube to gether with'the .assembledstock thereon maybe quickly inserted within the machine.` It is to 70' be understood that the axis of the threaded spin- ',dlels @extensive withthatofthe tube Ind withA those of the tubes lia. It is also understood that other means of forcing the rubberthrough thedie may be employed, such as pneumatic or hyfq draulic rams or pistons.

i la when removed from the machine becomes the,

To use the apparatus, the tube Ila is inserted vinto the rubber stock until it engages the closed end thereof whereupon the projecting end of the tube is placed within the saddle 42. At such time the neck of the stock is disposed between 5 the carriage `4I and the die 2i. y'Ihe motor is4 then started whereupon the operator guides the forward end of the stock into the die. He then places one end of a tube lia into a U-shaped saddle 4l' on the cross member 22 and manually guides the other end to receive the moving unit that has passed through the die. 'I'he position of the parts at such time is represented in Fig. 2. As soon as the stock has entered such tube. the operator is then free to place another .tube in the saddle ll-a on the crossmember 23 and guide it inthe same manner to receive the for# v wardly moving stock. 'Ihe same operationis repeated until all of the tubes for which the machine has been designed have been assembled. It is understood that lthe length of the inner tube and of the rubber stock'is such that at vthe completion of the operation the reduced neck' projects beyond the farmost end of the last outer tube. Thereupon, the unitary structure which comprises the tube Ila, the stretched rubber stock and the plurality of tubes Ila is lifted from the machine and the motor is reversed to return the carriage to its vinitial position. The assembled unit which is shown in Fig. 11 is then cut in'to sectionsas along the lines af-a, each having a length of the outer tube Ila so that the nnl ish'ed product corresponds to that shown in Fig. 4.' If desired however, the outer tube may comprise an elongated member from which sections may be cut transversely. In such case` the tube supports 22 and 23 would be eliminated and the tube would be supported on the end 33.

A modification of the-rubber stock is shown in IiFig.` wherein the forward end thereof is closed solely by the rubber wall which is reinforced by a'thickened portion Il to resist the str that are imparted to it during the, stretching operation. To facilitate the uniform distribution of forces against the rubber, I insert a plug el which is rounded to conform to the shape of the inner end wall of the stock, and which has an annular shoulder l! for receivingk the tube lea. Imayalsowishtoforcearigid ringv over the reduced end to reinforce the. rubberat this end in the stretching Operation.

' Figs. 14 to 20 illustrate modifications of the formation at the forward end of the `rubber j stock; In'Figs. 14 and 15, I have shown a relatively short metal sleeve or insert Il which is vulcanised in the rubber stock Il andis' arranged in abutting relation with the tube I0,-a. In Figs. -16 and 17 the forward end of the rubber stock is closed by a rubber wail 1I, which is reinforced by layers of fabric Il embedded therein. The rubber wan 1s of the form shown in ng. is is saditionally reinforced by a thickened rubber portion 11, to which'strength is-imparted by an embracing ring Il which comprises such portion of the To facilitate the distribution ot forces against thefrubber I have inserted a plug Il which is rounded to conform tothe shape of the inner end wall of the stock and which has-an annular shoulderfll for receiving the tube- |l-a.

In the mod ication illustrated in Figs. 18 and 19, I have vulcanined a sleeve Il in the forward portion of the stock which is. reduced in crosssectional area as indicated in such figures. The

'f sleeves are provided with inwardly turned anvu guiar flanges 82, against which a plug 88. abuts. As shown, these plugs conform in shape to the inner walls of their respective sleeves 8l, and to the adjacent inner walls of the rubber stock. The plugs 83 are likewise provided with annular shoulders for engaging the tube l0-a. In the form shown in Fig. 18, uniform distribution of the force against the rubber is facilitated by an angular rim of rubber formed integral with the walls of the tube. and lying in front of the angular ring 82 of the sleeve.

In the modification illustrated in Fig. 20, the forward end of the stock I5 is reduced in diameter. Inserted in this end of the stock is a plug 85, provided with an annular shoulder 88 to receive the tube Ill-a. Thestock is retained in contact with the plug 85, which is shaped to conform with the inner walls of the stock, by a cap 88 having a cup-likeA surface 81. The cap 86 is provided with a suitable opening 88 to receive a bolt 88, which threadingly engages the plug 85. and consequent upon the tightening of the bolt, the stock is gripped between the conical surface 81 of the cap and the outer surfaces of the plug 85.

In making the stock either in the form shown in Fig. 2 or in Fig. 5 the rubber is cured on a mandrel,.which is removed before the tube IIJ-a is inserted therein. In addition, the outer surfaces of the tube may be subjected to a grinding operation so that its wall thickness may be uniform throughout its length. Moreover, to facilitate the entrance of the stock into the die and also into the outer' tubes, I may apply lubricant yin the form of vaseline to the outer surface before the stock engages the die; I may also lubricate the outer surface of the inner member and .member and the inside surface of the outer member during the stretching operation, and thereby greatly assists in the uniform distribution of stresses throughout the length of the elastic material.

The reduction in size of the rubber stock through the die may comprise the only reduction employed, although if fdesired the stock may be reduced farther upon entering the outer tube. To facilitate the reduction, the opening of the die is tapered, as shownv7 at 85 and the wall of the tube lia is tapered as at 66. Due to the fact that` the forward end'of the advancing unit is unsupported, except by the die, the rubber is free to flow and hence the stretching stresses are distributed uniformly. As a result the nished resilient connection contains confined rubber, which ,is under a uniform state of stress to which it has been subjected during the forming operation, and hence the resilient connection is capable of withstanding a maximum number of oscillations without evidence of fatigue.

In Fig. 12, I have shown a cross-sectional view through a modified form of a finished article, wherein 50 designates ythe inner rigid member, 5i designates the outer rigid member, and 52 the intermediate layer of elastic material. In this illustration, the inner and outer members have a polygonal shape, and the inner member, in addition, is represented as being solid. If desired, however, the inner memberv may be hollow as heretofore described in connection with the article which is illustrated in Fig. 4.

lused in torsional connections.

The chief advantage of the article, which is made in accordance with the present method lies in the fact that the rubber or other elastic material has been placed in tension throughout the length of the article, and that a predetermined percentage elongation of the stock or material is maintained very uniformly vfrom one end to the other. The amount of stretch which may be obtained is Hunted only by the ultimate elongation of the elastic material, although it has been found that for ordinary torsional connections the amount of stretch need be only to 150% when rubber having a Shore durometer hard-l ness of 60 to 65 is used.

In Fig. `13, for example, there is shown a typical stress-stretch curve of theirubber that is usually The diagram in Fig. 12 shows the characteristics of the rubber when stresses up to` 1000 lbs. per sq. in. are placed upon it, this being the range that would cover the use of most resilient connections. The ultimate strength of the rubber however, may be as high as 4000 lbs. per sq. in. The solid line curve designated 55 in Fig. 13 illustrates the stress-stretch characteristic, whereas the broken line curve designated 56 shows the -stress-hardness characteristic of the rubber.

An inspection of the diagram in Fig. 13 shows that whenever the rubber is stretched an 'appreciable amount, the hardness, and therefore the internal, pressure, in the structure of the rubber increases. For example, according to the diagram, Whenever the rubber is stretched only the relative hardness is increased from 60 to 75% or a relative increase of 21%. The internal pressure in the structure of the rubber, as is evidenced by the increase in hardness, exerts a much .greater frictional force against the walls of the outer and inner rigid members of the resilient connection than would be possible if the rubber were not stretched. Moreover, the-fact that the rubber is stretched uniformly throughout the length of the article insures a high frictional engagement with the inner and outer meinbers of the resilient connection, and from one end to the other. In addition, the increase of internal pressure makes the rubber more resilient to torsional fatigue and more resistant to deformationy and more capable of withstanding high unit bearing pressures, such as are encountered, for example, in spring shackles of automobiles.

A further advantage of an article that ismade in accordance with the present method is the fact that the amount of stretch and likewise the stress which occurs in the rubber in the nished resilient connection can be predetermined. 4Conversely, the outside diameter of the free rubber tube can be predetermined whenever a definite amount of stretch is desired in the finished bushing. For example, if one desires p percentage stretch in the rubber of the nished bushing, then the-rubber mustA be stretched an amount equal to the product of (itu) 'and original length of the stock, and the cross sectional area of the free vtube will be the product of (ioo+ l) and the cross-sectional area of the rubber in the finished bushing.

Assuming that: v

1' equals the radius of the inside surface of the rubber in the finished bushing. R equals the radius of -the outside surface of the rubberin the finished bushing. Y

R.; equals the outside radius of the free rub- Y ber tube before the stretching operation. Then rR3-fr=the area of cross-section of rubber in the finished bushing.

The initial cross-sectional area=1rRi2n2 where (R1-r) represents the wall thickness of the free rubber tube, that isv to be stretched p percentage in order to completely ll the space be'- tween the ltwo metal members of the bushing.

Experience has shown that when "vaseline vhas been applied' to the outer surface of the inner member and to the inner surface of the outer member, as well as to the rubber tube that is tobe stretched, the rubber can be ,stretched very uniformly by this method. Then after a few hours have elapsed the rubber absorbs thefvaseline" and the frictional resistance to twisting of one member with respect to the other is withstood entirely by the rubber. Experiments have further shown that the stress applied at'the area of contact between the rubber andl theinside member is practically equal to the stress in the body lof the rubber; the action probably conforming to the law of iiuid friction, whereby the stress applied to the fiuidis exerted equally in all I directions.

Accordingly, I have provided a practical method of predetermining the frictional engagement be- .tween the rubber and the inner and outer members oi' the torsional bushing, and by this method sufficient stress can be placed in the rubber by a the rubber can be maintained very near to that calculated over long periods of time.

An important advantage, therefore, of articles which are made 'in accordance with thisvmethod f is that the stresses in the rubber and of the frictional engagement between the rubber and'the retaining members can be accurately calculated yin advance. A furtheradvantage of the method is the fact that the 'resilient connection may be made in any length and then cut to the desired size, or if desired, a large number of short bushingsmay be made at one time. The method, therefore, possesses economical manufacturing advantages and assures uniform distribution of stresses in the stretched rubber.

I claimzr 1. An article of manufacture comprising a preformed elastic stock body consisting of a tubulin` portion of .uniform diameter and an endV portion of gradually diminishing cross-sectional area ,extending from the main portion of the stock, a tapered plug in the body having its portion ofsmaller diameter extending into the' reduced end portion of the stock, and a reinforcing clamp surrounding said-reduced end of the stock. whereby thrust on said plugtis uniformly transmitted through said reinforced end portion the body of the stock. y

2. An article of manufacture comprising a preformed elastic'stock body consisting of a tubular portion of uniform diameter and a closed end portion of gradually diminishing cross-sectional area' 'extending from the main portion of the stock, a tapered plug in the body having its portion of smaller diameter extending into the reduced end portion of the stock, and'a reinforc.

ing clamp surrounding said reducedend o'f the stock, whereby thrust on said plug is uniformly transmitted through said reinforced end portion -to the body of the stock. v

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